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Description / Table of Contents: Abstract. Ideal evaluation of neuromuscular blockade can be done by mechanical or electromyographical registration of muscle contractions evoked by ulnar nerve stimulation. Unfortunately, devices needed for such registration are expensive or complicated to set up, and thus are not often used for routine monitoring in anaesthesia. In this study, we describe a simple and low-priced method permitting intra- and postoperative monitoring of neuromuscular blocking agents. The accuracy of plethysmomechanomyography (PMG) was evaluated by comparing simultaneous electromyographic (EMG) and plethysmographic measurements. Methods. For plethysmographic registration of muscle response to nerve stimulation a simple infusion system is twisted there to five times around one hand and connected to an anaesthetic monitor via a pressure transducer. The drip chamber is fixed about 20 cm above the hand (Fig. 1). Then, the infusion system is then filled up with physiologic saline solution and the clamp is nearly closed. Electric stimulation can be carried out using any nerve stimulator. Using this method, PMG mainly records the contractions of abductor digiti minimi muscle, but also partly those of the interossei. Evoked muscle contractions cause stretching of the infusion system, which leads to pressure changes proportional to the strength of contraction. The muscle response to "train-of-four" (TOF) stimulation of the ulnar nerve was recorded simultaneously by EMG and PMG in 11 patients (ASA class I or II) undergoing neurosurgical procedures and therefore requiring muscle relaxation. After induction of anaesthesia by injection of etomidate and fentanyl, supramaximal stimulation and control values (T0) were defined. Anaesthesia was maintained by supplementation with nitrous oxide/oxygen (1:2) and muscle relaxation was carried out with vecuronium. We used the integrated nerve stimulator of a Datex Relaxograph NMT-100 EMG monitor and proceeded to stimulate the ulnar nerve at the forearm with supramaximal strength. The PMG was registered by a Siemens Siredoc 220 printer connected to a Siemens Sirecust 1281 anaesthetic monitor. First twitch ratio (T1/T0) and TOF ratio (T4/T1) were calculated from these recordings. The EMG recordings were made by a Datex Relaxograph NMT-100 monitor, which automatically computes T1/T0 and T4/T1. The comparison of EMG and PMG values was carried out by simple linear regression. Statistical evaluation was performed using analysis of variance. Results. A plethysmographically registered graph of the TOF-evoked muscle response is illustrated in Fig. 2. Simultaneous EMG and PMG recordings of onset and recovery from a nondepolarizing blockade are shown in Fig. 3. A strong positive correlation (P〈0.001) of EMG and PMG was found with correlation coefficients of 0.98 for T1/T0 and of 0.97 for T4/T1. The mean difference between values of both methods was 5%, maximally 18% (T1/T0) and 20% (T4T1). Conclusions. Mechanomyography and EMG are well established methods of neuromuscular monitoring. Our data demonstrate that PMG provides a reliable measurement of neuromuscular transmission that correlates well with EMG. Since only materials of daily use in anaesthesia are needed, no substantial costs will arise when the plethysmographic method of measurement is used for routine anaesthetic monitoring.

Description / Table of Contents: Abstract. Monitoring of ventilation in infants is difficult and often not very reliable. In this study, transcutaneous measurement of blood gas tensions was used to investigate the influence of four different modes of ventilation on oxygenation and ventilation in anaesthetized infants. Methods. In a randomised study, transcutaneously measured PO2 (tcPO2) and PCO2 (tcPCO2) tensions were continuously registered in 42 ASA class I and II infants between 3 and 24 weeks of age undergoing minor surgical procedures (inguinal hernia repair). Two breathing systems combined with different modes of ventilation were evaluated: manual ventilation with Kuhn's T-piece system and face mask (group A; n=11) or endotracheal tube (group B; n=10); manual ventilation with paediatric circuit system and face mask (group C; n=11); and mechanical ventilation with paediatric circle system, endotracheal tube, and positive end-expiratory pressure (PEEP) 3 cm H2O (group D; n=10). Transcutaneous values were measured by a combined tcPO2/PCO2 electrode (E 5277, Radiometer). Anaesthesia was maintained by controlled ventilation with N2O/O2 (67%/33%) and halothane 0.5 – 1.5 vol.%. Surgical and anaesthetic techniques were standardized and the anaesthetist was blinded to the measured values. Results. Preoperative mean tcPO2 values while spontaneously breathing air ranged between 69 and 75 mm Hg in all patients. During anaesthesia and controlled ventilation (FiO2=0.33), there was a significant increase in tcPO2 (P〈0.01) in 3 groups: in groups A and D mean tcPO2 increased to 90 – 100 mm Hg and in group C to 110 – 120 mm Hg. In contrast, tcPO2 in group B reached only 75 – 80 mm Hg, which was not considered significant. Postoperatively, tcPO2 immediately reached baseline values in all patients (Fig. 2). Compared to preoperative values, the alveolar-tcPO2 difference (AtcDO2) significantly increased during anaesthesia in all groups (Fig. 3). The tcPCO2 measurements revealed marked alveolar dysventilation, with hyperventilation supervening in groups A, B, and D; in group C, however, most (7 of 11) infants were normoventilated (Fig. 4). Conclusions. Adverse effects of anaesthesia on pulmonary function in infants are caused by loss of the PEEP effect induced by the physiological subglottic stenosis. Endotracheal intubation and the increase in chest wall compliance during anaesthesia lead to a decrease in functional residual capacity (FRC) associated with premature airway closure and ventilation/perfusion mismatch. These pathophysiological disturbances result in a marked increase in AaDO2 and low arterial PO2 values despite high FiO2, as could be observed when intubated infants had been ventilated with a high-flow T-piece system (group B). Mechanical ventilation with a paediatric circuit system and endotracheal tube allows the use of low PEEP levels (group D), which may replace the lost subglottic function and partially restore the FRC. Ventilation by mask does not disturb the functional subglottic stenosis, and the impairment of pulmonary function will depend solely on the decrease in FRC caused by increased chest wall compliance (group A). If mask ventilation is combined with a paediatric circuit system (group C), the pressure relief valve produces a low PEEP of 2 to 3 cm H2O, which may partially counteract the decrease in FRC. With regard to oxygenation, the paediatric circle system proved to be superior to the high-flow T-piece system independent of whether children were ventilated via a face mask or an endotracheal tube. The group-specific differences in degree of dysventilation with manual ventilation show that the type of breathing system is important with regard to the size of the tidal volume delivered. Thus, tidal volumes will be unintentionally increased by the high fresh gas flow needed when a T-piece system is used. The lower flow and preadjusted pressure limit may prevent the delivery of excessive tidal volumes with the paediatric circuit system. The high incidence of dysventilation with mechanically controlled ventilation might be caused by the limited applicability of ventilation nomograms during anaesthesia for this age group.